“When you smash them with a hammer, they break into pieces and dust,” the Crystal Lake boy said.

The class is just one example of the sprucing up of summer programming being done by park districts and city parks and recreation departments throughout the county, offering new classes and expanding existing offerings.

The Crystal Lake Park District has had a flurry of interest in its programs and ran out of summer brochures within a month. The “Rock On!” class, for instance, has been offered for the past three years, but this was the first time enough people signed up to run it, outdoor education supervisor Jess Day said.

Declan, along with the seven other kids enrolled in “Rock On!”, learned multiple facts about rocks, such as how to describe them. They tested the shapes by throwing them down the steep hill next to the Nature Center – and then scrambling down after them to retrieve them.

They discovered which ones were soft and which ones couldn’t be scraped by a penny or the head of a screw. They described the rocks’ colors and then dunked them in water to see whether they changed. They learned about the different ways rocks are formed and looked at fossils, including a piece of the exoskeleton of an arthropleura, a giant relative of the centipede that could grow to 8.5 feet long.

And they wrapped up the class by mining chocolate chips from cookies.

The fast-paced class keeps the kids moving from place to place for the hour, managing to keep even a 5-year-old’s attention, said Declan’s father, John Malone.

“We both had fun,” he said. “It was a cute class. [Day] did a good job teaching.”

Day also runs a class designed to teach younger children about soil. Kids make mud pies while learning about the different soils and what they’re used for, he said.

Crystal Lake isn’t the only park district offering programs to keep kids busy this summer.

The Tween Night at Woodstock Water Works brings in between 150 and 175 fifth- through eight-graders every Wednesday, program coordinator Becky Vidales said.

One week “Jaws” was shown, another week a DJ was brought in, and another week had a glow-in-the-dark theme.

“It’s just someplace for tweens to go in the evenings,” Vidales said. “There’s no parents and no little kids. They have the place to themselves.”

The Huntley Park District is teaming up with the nonprofit A Place to Shine Music to offer a new music festival planned for July 20, part of expanded concert programming this year, said David Genty, the park district’s supervisor of marketing and special events.

In the past, three concerts were held each summer in Deicke Park, he said. This year, the park district is branching out, bringing performances to the different neighborhoods and adding more concerts.

Genty had heard so many covers – he doesn’t know how many times he’s heard Journey covers at summer festivals – that the new Discovery Music Fest is designed to feature original singer-songwriters.

“Music is one of those things that you hear wherever you go,” Genty said. “You walk down the street and you hear music. This is a chance to give up-and-coming musicians a chance to share their work, their art. It’s all original works, no covers.”

The Marengo Park District’s new recreation director, Kurt LaPak, took the reins in October, and one of the programs he added is the youth fishing program, as well as a roller hockey class that just finished up. He’s also trying to add more art classes to make up for some of the programs being cut in schools.

“I’m in charge of programs, and I’m a fisherman. I figured if I’m going to teach a class, it might as well be something I enjoy,” said LaPak, who said he learned how to fish from his dad and that a lot of fathers don’t have time to take their kids fishing anymore.

When the class started in June, he taught the kids about knot tying and how to cast reels. A few weeks later, five boys, ages 8 to 12, were braving the rain at the Rush Creek Conservation Area in Harvard, hoping to catch the largemouth bass, bluegill and green sunfish stocked in the pond.

Kyle Norcutt, 8, learned how to fish from his father and uncle.

“I like the way the fish kicks to the right and then the other way,” the Riley Elementary School student said.

He picked the fishing club and an engineering class – kids learn about simple machines using Legos – from the summer brochure mailed to his home.